This invention relates to an improvement in a double-heterostructure injection laser.
Since a double-heterostructure semiconductor, hereinafter referred to a DHS, laser diode has been developed, threshold currents have been prominently decreased and oscillations on a continuous wave basis at room temperature have become possible. One such laser is disclosed in U.S. Pat. No. 3,691,476. In a conventional DHS laser diode, as shown in FIG. 1, a GaAs active region 3 is sandwiched between an n-type Ga.sub.1.sub.-y Al.sub. y As region 2 and a p-type Ga.sub.1.sub.-y Al.sub. y .sub.'As region 4, in order to increase the probability of carrier recombination in the active region 3. Such a laser diode, as shown in FIG. 1, is made by sequential epitaxial growths of the first region 2 of n-type Ga.sub.1.sub.-y Al.sub. y As, the second region 3 of the GaAs, the third region 4 of p-type Ga.sub.1.sub.-y.sub.' Al.sub.y' As, and a fourth region 5 of the p-type GaAs, on an n-type GaAs substrate. Reference numeral 1' designates the ohmic contact face to contact an electrode, and reference numeral 1" designates a cleaved surface.
In order to reduce the threshold current experiments were conducted to select lattice constants having the active region and the neighboring regions about equal to each other. Satisfactory results were not obtained.